Question: Solve for $z$ : $4 + z = 7$
Explanation: Subtract $4$ from both sides: $ \begin{eqnarray} \\ 4 + z &=& 7 \\ \\ {-4} && {-4} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{4 + z} &\hphantom{=}& \hphantom{7} \\ z &=& 7 {- 4} \\ \end{eqnarray} $ Simplify. $ z = 3$